Example embodiments of inventive concepts relate to a signal processing technique, and more particularly, to auto gain controllers capable of improving a receiving performance and communication terminals having the same.
In a wireless transceiver system using a non-contact IC card, e.g., a smart card, such as Near Field Communication (NFC), amplitude of a RF signal transmitted or received between the non-contact IC card and a reader may be changed variably according to a distance between the non-contact IC card and the reader. Accordingly, the non-contact IC card and the reader may reduce a signal distortion by converting and transmitting the RF signal by using an analog to digital converter. In this case, for fixing amplitude of the RF signal varied according to the distance within an input range of the analog to digital converter, an auto gain controller (AGC) is used.
The AGC is a device keeping amplitude of an output signal constantly by controlling gain of an amplifier automatically, and it may perform a regular output by forming feedback loop, which may adjust a gain according to an amplitude level of an input signal. A wireless communication system using such an auto gain controller requires predetermined time or locking time structurally until an output signal is kept regularly. That is, the AGC may be used only in a wireless communication system capable of transmitting a RF signal where a preamble signal is included to lock the auto gain controller.
Generally, a wireless communication system, which may not use the auto gain controller, amplifies a RF signal by using a fixed gain amplifier having a fixed gain. In such a wireless communication system, when a gain value of the fixed gain amplifier is set high or a RF signal larger than expected is input, an output signal is out of an operation range of an analog to digital converter. Additionally, when a gain value is set lower to prevent the problem, receive sensitivity of entire wireless communication system is deteriorated.